The Demon  (1978)

Theatrical Release Information:
The Demon

Consumed by the jealousy and power struggles of their own relationships, a man, his mistress and his wife involve three children in their own games-with tragic results. After Sokichi stops providing his mistress with monetary support, she leaves her three children with him, whom she insists are also his, and disappears. Sokichi is bewildered and his wife is livid so with regard only for their own discomfort, they go about remedying their situation. ~ Cammila Albertson, All Movie Guide